The DNS - QA Monitor tests the ability of a Primary and the Secondary DNS server to respond to a record query, as well as its level of responsiveness.
The DNS - QA Monitor uses the Universal Datagram Protocol, which is the primary (more efficient) method of communication with DNS servers. UDP, unlike TCP, does not require acknowledgements of packets received.
The DNS - QA Monitor alternately queries both the Primary and the Secondary DNS server for a Domain Name until one of the DNS servers responds, or the "Maximum Test Duration" time expires.
The results of the Domain Name resolutions are compared against a list of expected IP addresses. Results are verified in one of two ways:
- The result set must include all of the IP addresses in the "expected" list
- The result set must have at least one of the IP addresses in the "expected" list
The DNS - QA Monitor considers the test to have failed:
- If the above noted tests fail
-or- - If both DNS Servers fail to respond within the "Maximum Test Duration"
The DNS - QA Monitor tests:
- That at least one DNS server is "up and running"
- That the Primary DNS server, Secondary DNS server or both are able to respond to a Domain Name Query, perform a lookup and resolve a hostname
- That the results of the resolved Domain Name correctly corresponds to the IP address you expect
- That the complete round trip time until the response is received is within a specific number of seconds
The Test Parameters dialog box is used to specify the location of the DNS Server you want to monitor, and any parameters required to connect to it.
IP Address
Enter the IP Addresses of your Primary and/or Secondary DNS server(s).
An example of a valid IP address is: 10.20.30.2
After entering your Primary IP Address, click the OR... button to add the IP Addresses of any number of secondary DNS servers.
UDP Port
Specify the Port Number that the DNS server responds on. By default, the standard Port Number used for DNS communication (Port 53) is already entered.
DNS Entry "A Record" to Query
The DNS - QA Monitor queries both the Primary and Secondary DNS servers in a round-robin manner, requesting a lookup for the Domain Name you enter.
Note: This must be an "A" Record. It cannot be a "CNAME" Record.
The Analysis of Test Results section is used to define a list of IP addresses you expect the Primary DNS server, Secondary DNS server, or both DNS servers to resolve for the DNS Entry.
Two types of test analyses are supported:
- Expect all of the following IP addresses. In this case, the DNS - QA Monitor requires the results to contain all the defined IP addresses for the Monitor to pass.
- Expect at least one of the following IP addresses. In this case, the DNS - QA Monitor requires only a single match in the defined IP addresses for the Monitor to pass.
Click the Or... button to add additional IP addresses. Results are analyzed using the Boolean OR operator.
The Update... button is used to test your configuration parameters before enabling the Monitor. For example: Contacting DNS Server(s): "10.200.50.2, 10.200.50.3" on UDP port 53 for "www.xyzcompany.com".
When the Monitor is in an Up state, test results are reported as shown in the example below:
rtt - Round-Trip Time. This value indicates the time it took the test packet to reach the monitored resource and return a response to ipMonitor. Round-trip time is measured in milliseconds (ms).
When the Monitor is in a Warn, Down, or Lost state, the Last Result field indicates the problem encountered. Different Monitor types generate specific Error Codes in accordance with the technical capabilities of the Monitor. Refer to the Error Codes section of this document for details.
The DNS - QA Monitor does not support CNAMEs. Canonical Name Records within the DNS database are used to indicate the true (or canonical) hostname of a computer when aliases are used to allow a machine to be known by more than one hostname. Instead, the DNS - QA Monitor requires that you enter an Address Record (A Record) to query, which maps the hostname of a machine directly to its numeric IP address.
For information on settings common to all Monitor types, such as Identification, Timing, Notification Control and Recovery Parameters, refer to General Monitor Settings.
The following error codes are generated by the DNS - QA Monitor. Error codes are displayed in Real-time and Historical Reports. They can also be added to Alerts using Tokens.
| Message | Details |
|---|---|
| Configuration information for this item is missing some required fields | A required element for Monitor connectivity or testing was not supplied to ipMonitor. |
| The remote device timed out before sending a response | The resource being monitored did not respond within the maximum allowable time. |
| The remote device provided an empty list of values | No data was returned from the remote server. |
| The returned query did not meet the specified parameters | The data returned did not match the expected result set as defined in the Monitor configuration. |
For information on other features and concepts related to those discussed in this article, refer to the following ipMonitor resources:
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Last Updated: March 30, 2007 | What did you think of this topic?